Inhibited Manganese Oxide Formation Hinders Cobalt Scavenging in the Ross Sea

Abstract

Phytoplankton productivity in the Southern Ocean is an important sink for CO 2 (Arrigo, Robinson, et al., 1999) and accounts for 5%-10% of total global oceanic primary production (Arrigo et al., 2008;Moore & Abbott, 2000). While the Southern Ocean is generally considered to be iron (Fe) and light-limited (Alder-

Diel Redox Cycle of Manganese in the Surface Arctic Ocean

“…In contrast, Mn oxidation is absent in the surface Sargasso Sea throughout the day and night, whereas it is present in the dark subsurface (Sunda & Huntsman, 1988). Oldham et al (2021) did not detect pMn(IV) formation in either sun-lit surface or dark subsurface waters in the Ross Sea. The conditions that govern the diel Mn redox cycle are not clear, but have important implications for availability of Mn and other pMn-associated micronutrients.…”

“…Factors such as temperature and microbial communities may lead to higher light‐dependent Mn reduction rates at the shelf stations compared to basin stations. Alternatively, given the high concentrations of humic substances in the Chukchi Sea (Hioki et al., 2014; Nakayama et al., 2011), it is possible that Mn oxidation at night was inhibited at shelf stations (6, 61, and 66) due to strong dissolved Mn(III)‐ligand complexes (Oldham et al., 2021). However, the inhibition of Mn oxidation cannot be a universal phenomenon in the Chukchi Sea, since slope Station 60 has a high AOS.…”

“…Oldham et al. (2021) did not detect pMn(IV) formation in either sun‐lit surface or dark subsurface waters in the Ross Sea. The conditions that govern the diel Mn redox cycle are not clear, but have important implications for availability of Mn and other pMn‐associated micronutrients.…”

“…We take advantage of sampling times that spanned a range of light conditions and relatively constant hydrographic parameters throughout the Polar Mixed Layer to reconstruct a pseudo‐diel cycle. This study is one of few that focuses on the oxidation state of pMn in the ocean (Hermans et al., 2019; Lee et al., 2021; Oldham et al., 2021), and the first one in the Arctic Ocean. Lee et al.…”

Seasonal Dynamics of Dissolved Iron on the Antarctic Continental Shelf: Late‐Fall Observations From the Terra Nova Bay and Ross Ice Shelf Polynyas

“…These observations imply that northwards export of SW might not constitute a major off-shelf flux of DFe in the western Ross Sea. Oldham et al (2021) have recently reported much higher concentrations of DMn in water column samples from the western Ross Sea compared to the values measured in our PIPERS samples and from previous studies that collected samples during austral spring and summer (Gerringa et al, 2020;Sedwick et al, 2000). For stations sampled in February-March 2018, including stations in Terra Nova Bay, Oldham et al (2021) report an average concentration of 10 ± 14 nM for total dissolved manganese, which was comprised of varying proportions of Mn(II) and organically complexed Mn(III); they suggest that these relatively high DMn concentrations may reflect the precipitation of dissolved Mn(III)-humic complexes upon acidification of filtered samples in previous studies.…”